Tumor necrosis factor (herein “TNF”) is a cytokine which produces a wide range of cellular activities. TNF causes an inflammatory response, which can be beneficial, such as in mounting an immune response to a pathogen, or when overexpressed can lead to other detrimental effects of inflammation.
The cellular effects of TNF are initiated by the binding of TNF to its receptors (TNF-Rs) on the surface of target cells. The isolation of polynucleotides encoding TNF-Rs and variant forms of such receptors has been described in European patent publication Nos. EP 308,378, EP 393,438, EP 433,900, EP 526,905 and EP 568,925; in PCT patent publication Nos. WO91/03553 and WO93/19777; and by Schall et al., Cell 61:361-370 (1990) (disclosing the P55 type TNF receptor). Processes for purification of TNF-Rs have also been disclosed in U.S. Pat. No. 5,296,592.
Native TNF-Rs are characterized by distinct extracellular, transmembrane and intracellular domains. The primary purpose of the extracellular domain is to present a binding site for TNF on the outside of the cell. When TNF is bound to the binding site, a “signal” is transmitted to the inside of the cell through the transmembrane and intracellular domains, indicating that binding has occurred. Transmission or “transduction” of the signal to the inside of the cell occurs by a change in conformation of the transmembrane and/or intracellular domains of the receptor. This signal is “received” by the binding of proteins and other molecules to the intracellular domain of the receptor, resulting in the effects seen upon TNF stimulation. Two distinct TNF receptors of −55 kd (“TNF-R1”) and −75 kd (“TNF-R2”) have been identified. Numerous studies with anti-TNF receptor antibodies have demonstrated that TNT-R1 is the receptor which signals the majority of the pleiotropic activities of TNF.
The domain required for signaling cytotoxicity and other TNF-mediated responses has been mapped to the −80 amino acid near the C-terminus of TNF-R1. This domain is therefore termed the “death domain” (hereinafter referred to as “TNF-R death domain”) (see, Tartaglia et al., Cell 74:845-853 (1993)). Other proteins have been identified which also have regions homologous to the TNF-R death domain. These regions are also referred to generically as “death domains.” Examples of proteins having such a death domain include Fas (Tartaglia et al., Cell 74: 845-853 (1993)), FADD (Chinnaiyan et al., Cell 81: 505-512 (1995)), RIP (Stanger et al., Cell 81: 513-523 (1995)), TRADD (Hsu et al., Cell 81: 495-504 (1995)), DR3 (Chinnaiyan et al., Science 274: 990-992 (1996)), and DR4 (Pan et al., Science, 276: 111-113 (1997)).
One activity produced by the interaction of TNF with TNF-R is cell death or apoptosis. It has been determined that the cell death process is mediated by the interaction of the death domains of TNF-R and other death domain-containing proteins. After binding of TNF to TNF-R, such proteins associate, forming homodimer and heterodimers, resulting in the instigation of the apoptotic process. As a result, inhibiting the interaction of death domain proteins will inhibit the induction of apoptosis.
It would, therefore, be desireable to identify new death domain-containing proteins which may be involved in the apoptotic process in order to in turn identify inhibitors of death domain associations and the apoptotic process resulting therefrom.